Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56, No. 4 (2013)
Journal homepage: http://constructii.utcluj.ro/ActaCivilEng
Special Issue: International Conference Sustainable Solutions for Energy and Environment-EENVIRO 2013.
Iron and manganese removal from difficult ground water sources
Gabriel Racoviteanu *1, Vulpasu Elena 2
1,2
Technical University of Civil Engineering of Bucharest (UTCB) Department of Hydrotechnical
Engineering, Faculty of Hydrotechnics, 124 Lacul Tei Blvd., 020396 Bucharest, Romania
(Accepted 11 October 2013; Published online 26 December 2013)
Abstract
A large part of the ground water sources from Romania contains iron and manganese in
concentration higher than the limits for drinking water. The presence of iron and manganese in
drinking water in high concentration determine color in the water and metallic taste. The paper
presents the pilot plant studies performed in the Technical University of Civil Engineering of
Bucharest, having the scope of iron and manganese removal from two ground water sources. One
of the sources is more complex and contains also ammonia, which complicates the treatment
procedures. The results of the experimental trials revealed that iron can be removed by oxidation
with air and rapid sand filtration up to concentration of 0.01 mg/l in the treated water, but for
manganese removal to concentration lower than 0.05 mg/l in the treated water it is necessary to
add potassium permanganate as complementary oxidant. When the raw water contains iron,
manganese and also ammonia, the treatment scheme is more complicated, the most important
criteria for obtaining good quality drinking water are:
 The order of the processes: iron and manganese removal come first and ammonia removal
secondly;
 Use of combined oxidation process by air and also potassium permanganate enhance the
manganese removal;
 Break-point chlorination represents an efficient procedure for ammonia removal. Though, the
high chlorine dose determines a risk related to THM formation, fact which requires an
adsorption on GAC. Another important aspect is that sufficient reaction time has to be achieved,
recommendable one hour.
Rezumat
O mare parte din sursele subterane de mica sau de mare adancime contin fier si mangan in
concentratii care depasesc limitele impuse pentru apa potabila. Prezenta fierului si manganului in
apa potabila confera apei culoare iar la concentratii ridicate gust metalic. Articolul prezinta
cercetarile efectuate in cadrul Universitatii Tehnice de Constructii Bucuresti in scopul indepartarii
fierului si manganului din doua surse de apa subterana. Una dintre surse este mai complexa,
contine amoniu ceea ce complica procedeele de tratare. Rezultatele experimentale au aratat ca
fierul poate fi retinut prin oxidare cu oxigenul din aer si filtrare pe nisip cuartos pana la
concentratii de 0.01 mg/l in apa tratata, insa pentru retinerea manganului pana la concentratii mai
mici de 0.05 mg/l in apa tratata este necesara adaugarea permanganatului de potasiu, ca oxidant
suplimentar. In situatiile in care apa bruta contine atat fier si mangan cat si amoniu, schema de
tratare este mai complicate, cele mai importante criterii pentru obtinerea unei bune calitati a apei
potabile sunt:
*
Corresponding author: Tel./ Fax.:021-2423595
E-mail address: [email protected]
Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32



ordinea proceselor: indepartarea fierului si manganului in prima faza si oxidarea amoniului in
faza a doua;
utilizarea unor procese de oxidare combinate cu utilizarea aerului si a permanganatului de
potasiu care imbunatateste eficienta de reducere a manganului;
clorinarea la break-point reprezinta un proces eficient pentru reducerea amoniului. Deoarece
doze mari de clor determina un risc privind formarea THM este necesara adsorbtia pe CAG.
Un alt aspect important este un timp de reactie suficient, recomandabil o ora.
Keywords: iron, manganese, ammonia, water treatment.
1. Introduction
The experimental researches were performed on a pilot plant for the water sampled from two
ground water sources: Fetesti and Tandarei. It should be mentioned that the quality of both sources
reveal iron and manganese over the limits. In Tandarei ammonia concentration are also over passed,
which generates even more difficulties in the treatment process.
The localization of the water sources is presented in Fig. 1.
Figure 1. Water sources localization (source: http://www.rotravel.com).
The first step in iron removal will be based on oxidation of the divalent iron using oxygen provided
from the air [1,2]. If necessary, it can be supplemented by adding a number of other treatments such
as: pH correction, chemical oxidation, flocculation, clarification. Ozone and potassium
permanganate are the best supplementary oxidants, especially when complex iron is present. When
the water contains high levels of organic matters and manganese, the amount to be dosed is to be
identified experimentally if possible.
Manganese Mn2+ is very slowly oxidized by oxygen to form MnO2. The manganese dioxide will
react as catalyst. However, this effect will not be enough to produce treated water that is completely
manganese free.
In practice, instead of "manganising" sand, it is advisable to use a filtration media of MnO2 (green
manganised sand) that can be mixed in greater or lesser amounts with the regular sand and which
will also require regeneration at regular intervals.
Ammonia removal can be reached by biological processes or by oxidation chlorine when the
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
amount of chlorine dosed rises above the critical point. However, disinfection by-products
(chlorinated compounds, THMs) often appear when precursors (natural organic matter - NOM)
occur in raw water. The presence of THMs in drinking water is not desirable due to high
carcinogenic risk. Therefore, this technique only applies when the raw water contains low amounts
of precursors (NOM).
Chlorine is the single effective chemical for elimination of nitrogen ammonia present in the raw
water in the molecular form NH3, but also in the ionic form NH4+.
2. Materials and methods - description of the pilot plant
A pilot plant belonging to the Faculty of Hydrotechnics, UTCB was used for the research. The main
characteristics of the pilot plant are:
 pre-oxidation contact tank, having a water column height of 4 m; different contact times
can be provided in the range of 8 – 30 min.;
 rapid sand filter, with a mono-granular layer having the height of H=1.2.m; the filtration
velocity can be varied from 4 m/h to 15 m/h;
 chemical preparation and dosing which includes dosing pumps and storage tanks;
 treated water reservoir having the volume of V=300 dm3;
 backwash water installation consisting of reservoir, backwash water pump and air blower.
Several oxidizing agents have been used during the experimental trials: compressed air, potassium
permanganate and sodium hypochlorite. Fig. 2 presents an image of the plant.
Figure 2. Water Treatment Pilot Plant, UTCB.
3. Results and discussions
3.1 Assessment of the raw water quality
The evaluation of the raw water quality was performed in several stages of sampling from both
sources (Fetesti and Tandarei). The average values are presented in Table 1.
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
Table 1. Raw water quality
Item
Parameter
Unit
units
µS/cm
mequiv/l
Hardness
degrees
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg KMnO4/l
Fetesti
Source
7.82
745
5.5
Tandarei
Source
8.05
1249
6.1
Maximum admissible
values*
6.5 – 9.5
2500
-
16.52
21.28
min. 5
64
32.8
0
7.4
335.5
131.35
0.17
0.140
26
1.12
84
41.31
0.88
1
372.1
132.06
0.24
0.156
116
2.21
0.5
50
250
0.2
0.05
250
20
no abnormal changes
and acceptable to
consumers
1
10
5
50
0.1
1
10
1
2
3
pH
Conductivity
Alkalinity
4
Total hardness
5
6
7
8
9
10
11
12
13
14
Calcium
Magnesium
Ammonia
Nitrates
Bicarbonates
Chlorides
Iron
Manganese
Sulphates
Organic matter
15
Total organic
carbon
mg/l
1.6
2.9
16
17
18
19
20
21
22
Turbidity
Arsenic
Cadmium
Total chromium
Copper
Mercury
Lead
NTU
µg/l
µg/l
µg/l
mg/l
µg/l
µg/l
0.76
<0.2
<0.4
<0.5
<0.0006
<1
<1
0.7
<0.2
<0.4
<0.5
<0.0006
<1
<1
Note: * Maximum admissible values, according to the Drinking Water Law (458/2002, 311/2004) [4] and EU Directive
98/83/EC, 1998 [3].
The raw water analysis reveals the following:
 Both sources correspond to the required drinking water quality, except the following:
o For Fetesti the manganese concentration registers 0.14 mg/l compared to the
maximum admissible value of 0.05 mg/l;
o For Tandarei several parameters are over passed:
 The ammonia concentration registers a value of 0.88 mg/l versus 0.5 mg/l –
the maximum admissible value;
 The iron concentration registers a value of 0.24 mg/l versus 0.2 mg/l – the
maximum admissible value;
 The manganese concentration registers a value of 0.156 mg/l versus 0.05 mg/l
– the maximum admissible value;
 Both sources register low TOC concentrations, fact which reveal that the THM formation
potential is consequently low and chlorination is a viable process;
 The mineralization is normal for both sources;
 The pH registers neutral to light alkaline values in both sources.
3.2 Experimental trials on Fetesti water source
For the Fetesti source there were performed two experimental trials according to the treatment
schemes presented in the Fig. 3. Both schemes are conventional treatment schemes for iron
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
removal. The main difference between the schemes consist of iron oxidation which has been made
using air in the first trial while in the second experimental trial it has been used air + KMnO4.
Experimental trial no.1
Experimental trial no. 2
Raw water
Raw water
RAW WATER TANK
RAW WATER TANK
Air
Air + KMnO4 (0.25 mg/l)
AIR CONTACT TANK
AIR CONTACT TANK
Tc=20 min.
Tc=20 min.
3
3
Q =320 dm /h
Q =360 dm /h
RAPID SAND FILTER
RAPID SAND FILTER
vF = 5.0 m/h
vF = 5.0 m/h
Sodium
hypochlorite (0.5 mg/l)
Sodium hypochlorite (0.5 mg/l)
CHLORINE CONTACT TANK
CHLORINE CONTACT TANK
Tc=30 min.
Tc=30 min.
Figure 3. Technological schemes during experimental trials – Fetesti water source.
The experimental results revealed that iron concentration can be reduced up to 0.022 mg/l by air
oxidation and rapid sand filtration but the concentration of manganese can be reduced only up to
0.085 mg/l which is not satisfactory, having in mind the value of 0.05 mg/l – the maximum value
for drinking water according to Law 458/2002 (removal efficiency – 37.12%).
For this reason, in trial no. 2 it has been added potassium permanganate for manganese oxidation.
The main reasons for using potassium permanganate are (EPA, 1999):
 Potassium permanganate is a manganese oxidation specific reagent;
 It reacts with high efficiency at high pH values;
 The use of potassium permanganate has a low potential for by-products formation;
 The manganese is totally oxidized if the reaction time is enough;
 Overdosing of potassium permanganate gives to water a pink color which is immediately
observable;
 The insoluble MnO2 can be easy retained by rapid sand filtration;
 The insoluble MnO2 reacts as catalyst and has the ability to adsorb other ions from water
(Fe2+, Mn2+, Ra2+) increasing the removal efficiency of these ions; Also, insoluble MnO2 has
the ability to adsorb the natural organic matters from water, which represents the precursors
for THM formation in disinfection process;
 The KMnO4 doses are low: 0.94 (mg KMnO4/ mg Fe) and 1.92 (mg KMnO4/mg Mn)
respectively.
Fig. 4 a, b presents images during the experimental trials. It can be observed that during the
experimental trial no. 2 (with potassium permanganate added), the pre-oxidized water is slightly
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
colored because manganese dioxide is formed.
a
b
Figure 4. Pre-oxidation tank: a. trial 1 – oxidation by air; b. trial 2 – oxidation by air and potassium
permanganate
Figs. 5 and 6 present the experimental results for the both experimental trials. The analysis of
experimental results revealed the followings:
 the concentration of iron decreased from 0.17 mg/l for raw water to 0.01 mg/l for treated
water in the case of oxidation with air and potassium permanganate (removal efficiency –
92.94%);
 the concentration of manganese decreased from 0.14 mg/l for raw water to 0.014 mg/l for
treated water (removal efficiency – 90%).
100
0.3
Law 458/2002 - Fe
90
Mn
80
Removal Efficiencies(%)
0.25
Fe
mg/l
0.2
0.15
0.1
Law 458/2002 - Mn
0.05
Fe
Mn
70
60
50
40
30
20
10
0
0
AB
AB
AFRN11
AFRN
AFRN
1 1
AFRN
AFRN22
Figure 5. Variation of concentrations of iron and
manganese. AB – Raw water; AFRN1 – rapid
sand filtered water – trial 1; AFRN2 – rapid
sand filtrated water – trial 2.
AFRN
2 2
Figure 6. Variations of the removal efficiencies
for iron and manganese. AFRN1 – rapid sand
filtered water – trial 1; AFRN2 – rapid sand
filtered water – trial 2.
The results of experimental researches revealed the fact that the removal of iron from water can be
achieved by oxidation with air and rapid sand filtration up to concentrations lower that the imposed
value for drinking water by enforcement legislation, while for an efficient removal of manganese it
is necessary to add potassium permanganate to act as a catalyst.
3.3 Experimental trials on Tandarei water source
Because the raw water had the concentration of ammonia higher than the maximum value imposed
for drinking water (0.99 mg/l towards 0.5 mg/l according to Law 458/2002) it was selected chlorine
oxidation.
During the experimental trial no. 1, the technological scheme consisted of:
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32

pre-oxidation with sodium hypochlorite - 8.5 mg Cl2/l (chlorine dose was determined
experimentally by performing a break-point chlorination curve);
 rapid sand filtration for iron and manganese removal.
Fig. 7 presents the technological scheme during the experimental trial no. 1. The experimental
results revealed the followings:
 the chlorine oxidation and rapid sand filtration determined an iron concentration of 0.01
mg/l related to 0.2 mg/l the maximum value imposed for drinking water; the removal
efficiency was 97.22%. It should be noted that since the first hour of pilot plant operating,
the iron concentration was 0,01 mg/l;
 the manganese was removed from 0.22 mg/l for raw water to 0.07 mg/l for treated water
towards 0.05 mg/l the maximum value imposed for drinking water by Law 458/2002, which
it was considered not satisfactory;
 the ammonia concentration was 0.1 mg/l in the treated water related to 0.94 mg/l for the raw
water and 0.5 mg/l the maximum value imposed for drinking water.
 the free chlorine concentration was 0.19 mg/l and the total chlorine concentration was 0.31
mg/l. This revealed that the chlorine fully reacted with ammonia and the chloramines
concentration was low.
Raw water
RAW WATER TANK
Sodium hypochlotite (8.5 mg Cl2/l)
CHLORINE CONTACT TANK
Tc=30 min.
3
Q =200 dm /h
RAPID SAND FILTER
vF = 3.2 m/h
Figure 7. Technological scheme – experimental trial no.1 – Tandarei source.
Fig. 8 presents the results of experimentally determination.
1.00
Fe
0.90
Mn
0.80
Ammonium
mg/l
0.70
0.60
Law 458/2002 - NH4+
0.50
0.40
0.30
Law 458/2002 - Fe
0.20
Law 458/2002 - Mn
0.10
0.00
AFRN
AFRN1
AB
AB
Figure 8. The variations of iron, manganese and ammonia concentrations – experimental trial no.1.
AB – raw water; AFRN – rapid sand filtered water.
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
It can be concluded that the use of chlorine in the pre-oxidation process for removal of all three
compounds does not lead to a good quality of the treated water. The determination of chlorine doses
and the control of the process are difficult. Because the concentration of the manganese in treated
water was higher than the maximum value imposed for drinking water, in the experimental trial no.
2 it was selected a two stages water treatment scheme:
 iron and manganese removal by oxidation with air and potassium permanganate;
 ammonia removal by break point chlorination.
The technological scheme for this experimental trial is presented in Fig.9.
Figure 9. Technological scheme – experimental trial no. 2 – Tandarei water source.
0.50
0.25
0.40
0.20
Mn (mg/l)
Fe (mg/l)
Figs. 11 and 12 present the results of the experimental trials.
0.30
Law 458/2002 - Fe
0.20
0.15
0.10
Law 458/2002 - Mn
0.05
0.10
0.00
0.00
0
AB
1
AFRN
2
APox.
3
AFCAG
4
Figure 11. The variation of the iron
concentration on technological scheme – trial
no. 2. AB – raw water; AFRN – rapid sand
filtered water; APox. – post-oxidated water;
AFCAG – GAC filtrated water.
0
5
AB
1
AFRN
2
APox.
3
AFCAG
4
5
Figure 12. The variation of the manganese
concentration on technological scheme – trial no.
2. AB – raw water; AFRN – rapid sand filtered
water; APox. – post-oxidated water; AFCAG –
GAC filtrated water.
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
The concentration of iron decreased from 0.42 mg/l in the raw water to 0.01 mg/l for treated water
by oxidation with air and potassium permanganate and rapid sand filtration. The removal efficiency
was 97.6%.
The concentration of manganese decreased from 0.211 mg/l for raw water to 0.03 mg/l for rapid
sand filtered water and to 0.01 mg/l for water treated with sodium hypochlorite and granular
activated carbon (GAC) filtered towards 0.05 mg/l, the maximum admissible value for drinking
water.
1.0
0.9
NH4+ (mg/l)
0.8
0.7
0.6
Law 458/2002 - NH4+
0.5
0.4
0
AB
1
AFRN
2
APox.
3
AFCAG
4
5
Figure 13. The variation of the ammonia on technological scheme – trial no.2. AB – raw water;
AFRN – rapid sand filtered water; APox. – post-oxidated water; AFCAG – GAC filtrated water
Regarding ammonia removal, the technological scheme did not achieve a sufficient quality of the
treated water. The concentration of ammonia for the post-oxidized water with sodium hypochlorite
was 0.54 mg/l instead of the maximum admissible value of 0.5 mg/l (Fig.13). The GAC filtration
unit was inserted to remove the eventual reaction by-products formed (chloramines).
The concentration of free chlorine for the post-oxidized water was 0.31 mg/l and the concentration
of total chlorine was 0.94 mg/l. Because in the treated water exists in the same time free chlorine,
ammonia but also a relatively high concentration of total chlorine it is considered that the reaction
and treatment was insufficient.
The reaction time was around 30 minutes in the post-oxidation tank. From the post-oxidation tank
the water was passed through the granular activated carbon filter where, the free and total chlorine
were totally removed.
Fig. 14 presents the removal efficiencies of the three parameters of interest. It can be noticed that
for iron and manganese the removal efficiencies were higher than 85% and the removal efficiency
for ammonia registered a value of only 45%, insufficient for a good quality drinking water.
The treatment scheme of the 3rd experimental trial was the same as in the 2nd experimental trial
except the reaction time in the post-oxidation contactor, which was doubled. By doubling the
reaction time in post – oxidation process (experimental trial no. 3) it resulted a concentration of the
ammonia in the treated water of 0.1 mg/l which is lower than 0.5 mg/l, the maximum value imposed
for drinking water by Law 458/2002 (fig. 15).
The average concentration of free chlorine was 0.17 mg/l and the total chlorine 0.65 mg/l in the
rapid sand filtered water and it was fully retained on granular activated filter.
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
1.0
100
AFRN
90
0.8
70
0.7
60
0.6
NH4+ (mg/l)
Removal efficiencies(%)
0.9
APox
80
50
40
30
Law 458/2002 - NH4+
0.5
0.4
0.3
20
0.2
10
0.1
0
Fe
1
Mn
2
0.0
NH
3 4+
0
Figure 14. The removal efficiencies of interest
parameters – esperimental trial no.2. AFRN –
rapid sand filtered water; APox. – post-oxidated
water.
AB
1
AFRN
2
APox.
3
AFCAG
4
5
Figure 15. Variation of the ammonia
concentration on technological scheme –
experimental trial no.3. AB – raw water;
AFRN – rapid sand filtered water; APox. –
post-oxidized water; AFCAG – granular
activated carbon filtered water.
4. Conclusions
The experimental researches revealed the following:
 When manganese registers high concentrations in the raw water, simple air oxidation
does not respond for an efficient removal. Addition of potassium permanganate can
solve the problem due to the catalytic effect;
 When the raw water contains iron, manganese and also ammonia, the treatment scheme
is more complicated and as we could observe, the most important criteria for obtaining
good quality drinking water are:
o The order of the processes: iron and manganese removal come first and ammonia
removal secondly;
o Use of combined oxidative processes by air diffusion and also potassium
permanganate enhance the manganese removal;
o Break-point chlorination represents an efficient procedure for ammonia removal.
Though, the high chlorine dose determines a risk related to THM formation, fact
which requires an adsorption on GAC. Another important aspect is that sufficient
reaction time has to be achieved, recommendable one hour.
The kinetics of the processes for iron and manganese and also of the ammonia removal are well
known in the case in which one of the above mentioned products are presented in water. The
problem becomes much more complicated in the case in which all products are present in the same
time. The efficiency of the treatment process becomes very low if the correct order of the processes
and correct treatment reagents are not respected.
The research presented in the paper brings an important contribution on establishing the correct
order of the treatment processes for difficult groundwater containing high concentrations of iron,
manganese together with ammonia. When iron and manganese occurs in the source together with
amonia, the most efficient order of the process is iron and manganese removal using oxidative
processes enhanced by potassium permanganate catalytic effect and followed by breakpoint
chlorination for ammonia oxidation and removal.
The results of the pilot plant studies have been used to implement the treatment schemes for two
water supplies in Romania.
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Gabriel Racoviteanu, Vulpasu Elena / Acta Technica Napocensis: Civil Engineering & Architecture Vol. 56 No 4 (2013) 22-32
5. References
[1] Degremont - Water treatment handbook – Seventh edition, ISBN 978-2-7430-0970-0, France, 2007.
[2] Mănescu A., Sandu M., Ianculescu O. - Alimentări cu apă, 1994, Editura Didactică şi Pedagogică,
Bucureşti.
[3] Directiva 98/83/EC - Calitatea apei destinate consumului uman; on line la http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=DD:15:04:31998L0083:RO:PDF
[4] Legea 458/2002 M.O. Nr. 552/29 iulie 2002 - Legea privind calitatea apei potabile cu completarile si
modificarile ulterioare.
[5] EPA, (1999), Guidance Manual Alternative Disinfectants and Oxidants, on line la
http://www.epa.gov/ogwdw/mdbp/alternative_disinfectants_guidance.pdf
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